State Law.

The Washington State Department of Transportation (WSDOT) and local authorities are authorized to designate any portion of a highway under their respective jurisdictions for the exclusive or preferential use of:  (1) public transportation vehicles; (2) motorcycles; (3) private motor vehicles carrying a specified minimum number of passengers; and (4) certain categories of private transportation provider vehicles if the vehicles have a carrying capacity of at least eight passengers.  The portion of highways with these restricted usage rules are known as high-occupancy vehicle (HOV) lanes.
 
The WSDOT and local authorities have the ability to specify certain times of days or certain specified days during which the HOV restrictions are in effect.  The WSDOT and local authorities are also authorized to prohibit the use of an HOV lane by private transportation provider vehicles when the average transit speed in the HOV lane fails to meet United States Department of Transportation standards (falling below 45 miles per hour at least 90 percent of the time during peak hours).
 
Under current state administrative rule, the following motor vehicles are authorized to use the HOV lanes on interstate highways, state highways, and ramps:  (1) municipal transit vehicles; (2) buses with a carrying capacity of 16 or more people; (3) motorcycles; (4) all vehicles meeting specified HOV-lane occupancy requirements (except for trucks with more than a 10,000 pounds maximum operating weight rating); and (5) officially marked law enforcement and fire department vehicles equipped with emergency lights and sirens that are operated by on-duty Washington State Patrol or local law enforcement or local or special district fire department personnel.
 
In the 2020 Supplemental Transportation Budget, a budget proviso requires the WSDOT to provide access to HOV lanes to:

1. certain categories of private transportation provider vehicles if the vehicles have a carrying capacity of at least eight passengers;
2. vehicles that deliver or collect blood, tissue, or blood components for a blood-collecting or distributing establishment that are clearly and identifiably marked on all sides of the vehicles, which are considered emergency vehicles for this purpose; and
3. organ transport vehicles transporting a time-urgent organ for an organ procurement organization that are clearly and identifiably marked on all sides of the vehicle, which are also considered emergency vehicles for this purpose.

 
Federal Law.
 
Federal law applies to federal-aid highways, and requires that the HOV lanes be restricted for the use of vehicles with no fewer than two occupants per vehicle, subject to certain exceptions.  A public authority has jurisdiction over the operation of an HOV facility and may establish occupancy requirements of vehicles operating on the facility, so long as it complies with federal occupancy and usage restrictions.

Exceptions are granted to the following vehicles, subject to a public authority authorizing their use on an HOV facility within its jurisdiction:  (1) public transportation vehicles; (2) motorcycles and bicycles; (3) over-the-road buses serving the public; (4) high-occupancy toll vehicles; and (5) low emission and energy-efficient vehicles.
 
A "public transportation vehicle" is defined as a vehicle that provides designated public transportation or public school transportation and is owned or operated by a public entity, operated under a contract with a public entity, or operated pursuant to a license with a public authority to provide motorbus or school vehicle transportation services to the public.  An "over-the-road bus" is defined as a bus with an elevated passenger deck located over a baggage compartment.
 
While the state is not mandated to comply with federal HOV-lane requirements, if the Federal Highway Administration (FHWA) were to find a state to be out of compliance with its HOV-lane requirements, the FHWA could withhold payment to the state of federal funds.

The Washington State Department of Transportation may exempt for hire non-emergency medical transportation (NEMT) vehicles from HOV-lane vehicle occupancy requirements when the vehicles are in use for medical purposes.
 
A "for hire NEMT vehicle" is a vehicle that is a for hire vehicle that provides non-emergency medical transportation, including life-sustaining transportation purposes, to meet the medical transportation needs of individuals traveling to medical practices and clinics, cancer centers, dialysis facilities, hospitals, and other care providers.  A "for hire vehicle" means any motor vehicle used for the transportation of persons for compensation, except auto stages and ride-sharing vehicles. 
 
The owner of a for hire NEMT vehicle may apply to the Department of Licensing (DOL), county auditor or other agent, or subagent appointed by the Director of the DOL, for an HOV-exempt decal for a for hire NEMT vehicle.  The HOV-exempt decal allows the for hire NEMT vehicle to use an HOV lane.  For the exemption to apply, the decal must be displayed from the vehicle so that it is clearly visible from outside the vehicle and must be visible from the rear of the vehicle.
 
The owner of a for hire NEMT or the owner's representative must apply for an HOV-exempt decal on a form provided or approved by the DOL.  The application must include:

• the name and address of the person who is the owner of the vehicle;
• a full description of the vehicle, including its make, model, year, and the vehicle identification number;
• the purpose for which the vehicle is principally used; and
• other information as required by the DOL at the time of application.

 
The DOL, county auditor or other agent, or subagent, is required to collect a $5 fee when issuing a decal under this section, in addition to any other fees and taxes required by law.  An HOV-exempt decal may not be renewed.  The status as an exempt vehicle continues until suspended or revoked for misuse, or when the vehicle is no longer used as a for hire NEMT vehicle.
 
The DOL may adopt rules for HOV-exempt decal administration.